Human languages often disallow bare nominals as predicates. Scottish Gaelic is a particularly striking case, in that it disallows simple nominal predication entirely, using alternative syntactic means to deliver the required meanings. This paper provides an answer both to the larger question of why NP predication is so restricted, and to the more local one of why Gaelic uses the particular syntactic forms it does, based on a principle that regulates the interface between syntax and semantics: syntactic predicates must have open eventuality variables.